ANAEROBIC-DIGESTION OF COFFEE WASTE BY 2-PHASE METHANE FERMENTATION WITH SLURRY-STATE LIQUEFACTION

Anaerobic digestion of components of coffee waste was investigated. When the coffee waste was treated by a liquefaction process only, the degradation efficiency was 42%, taking into account the soluble materials that adhered to the surface of the waste. However, in a two-phase anaerobic digestion system consisting of liquefaction and gasification processes, the degradation efficiency increased to 70%. The components of coffee waste, namely, materials that could be eluted by a mixture of alcohol and benzene (hereafter called alcohol-benzene soluble materials), holocellulose and lignin, were degraded by 91%, 70% and 45%, respectively. The gas yield was 451 ml/g degraded coffee waste and 28.2% of the carbon in the waste was converted to biogas. The methane content in the gas evolved from the gasification reactor was high, being 66% (v/v).